linux-kernel - Re: [Stable-review] [22/68] ixgbe: prevent speculative processing of descriptors before ready

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Date:	Tue, 01 Mar 2011 02:14:33 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Greg KH <gregkh@...e.de>
Cc:	linux-kernel@...r.kernel.org, stable@...nel.org,
	Don Skidmore <donald.c.skidmore@...el.com>,
	Milton Miller <miltonm@....com>,
	"David S. Miller" <davem@...emloft.net>,
	Anton Blanchard <anton@...ba.org>, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org, stable-review@...nel.org,
	alan@...rguk.ukuu.org.uk,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Subject: Re: [Stable-review] [22/68] ixgbe: prevent speculative processing
 of descriptors before ready

On Mon, 2011-02-28 at 08:22 -0800, Greg KH wrote:
> 2.6.32-longterm review patch.  If anyone has any objections, please let us know.
> 
> ------------------
> 
> From: Milton Miller <miltonm@....com>
> 
> commit 3c945e5b3719bcc18c6ddd31bbcae8ef94f3d19a upstream.
> 
> The PowerPC architecture does not require loads to independent bytes to be
> ordered without adding an explicit barrier.
> 
> In ixgbe_clean_rx_irq we load the status bit then load the packet data.
> With packet split disabled if these loads go out of order we get a
> stale packet, but we will notice the bad sequence numbers and drop it.
> 
> The problem occurs with packet split enabled where the TCP/IP header and data
> are in different descriptors. If the reads go out of order we may have data
> that doesn't match the TCP/IP header. Since we use hardware checksumming this
> bad data is never verified and it makes it all the way to the application.
[...]

Packet splitting should be completely disabled on the 82599, anyway.
Greg, what happened to this patch:

commit a124339ad28389093ed15eca990d39c51c5736cc
Author: Don Skidmore <donald.c.skidmore@...el.com>
Date:   Tue Jan 18 22:53:47 2011 +0000

    ixgbe: fix for 82599 erratum on Header Splitting
    
    We have found a hardware erratum on 82599 hardware that can lead to
    unpredictable behavior when Header Splitting mode is enabled.  So
    we are no longer enabling this feature on affected hardware.
    
    Please see the 82599 Specification Update for more information.
    
    CC: stable@...nel.org
    Signed-off-by: Don Skidmore <donald.c.skidmore@...el.com>
    Tested-by: Stephen Ko <stephen.s.ko@...el.com>
    Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>

Ben.

-- 
Ben Hutchings
Once a job is fouled up, anything done to improve it makes it worse.

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